The present invention relates to a high-intensity discharge lamp lighting device and a lighting system, which is able to start lighting the high-intensity discharge lamp with compact lighting circuit means.
Recently, a compact metal halide lamp with a lighting power in a range of 10-30 W has been developed as a light source for optical fibers or a light source for halogen light bulb substitution. In such a metal halide lamp, the lighting efficiency is three or four times that the halogen light bulb, and remarkably smaller than the fluorescent lamp so as to be used as the light source.
Accordingly, the metal halide lamp as mentioned above is a light source having the advantages of the halogen light bulb and the electric bulb fluorescent lamp. However, since it is a high-intensity discharge lamp, it needs a stabilizer, i.e., lighting circuit means incorporating therein an igniter for generating a relatively high pulse voltage at the starting operation or lighting circuit means not incorporating therein an igniter, and an igniter separated from the lighting circuit means. As a matter of course, though the fluorescent lamp also needs lighting circuit means since it is also the discharge lamp, lighting circuit means of the high-intensity discharge lamp is overwhelmingly large in comparison with that of the electric bulb fluorescent lamp. Thus, even though a compact high-intensity discharge lamp would be developed for all troubles, an overall system containing a light source, a stabilizer, i.e., lighting circuit means and a lighting apparatus unwillingly has a large size.
To solve the above problem, the inventor has contemplated using a lighting circuit means principally comprising a compact high-frequency inverter, which is used for the fluorescent lamp especially for the electric bulb fluorescent lamp. This lighting circuit means for the electric bulb shaped fluorescent lamp is generally simple in its circuit arrangement, and works at a high-frequency. Accordingly, such a stabilizer is compact, light in weight and less-expensive.
However, when a high-intensity discharge lamp is lighted using such compact lighting circuit means for the fluorescent lamp, an intense blackening occurs at a starting operation.
As a result, the inventor has made investigations in detail about the cause and the measure of the blackening, and the following conclusions have been obtained. (1) Materials of the blackening are principally constituted by tungsten constituting electrodes.
(2) The blackening is caused by the fact that the tungsten of the electrodes evaporates at the starting operation, especially at the glow-arc transition. Then the tungsten sticks on the inner surface of the light-transmissive ceramic discharge enclosure.
Further to the conclusion, it is clarified that as a result of another investigation about the behavior of the electrode at the glow-arc transition in comparison with the lighting circuit of the conventional high-intensity discharge lamp which does not cause such a blackening at the starting operation, the blackening is caused by the difference of load characteristics between the fluorescent lamp lighting circuit and the high-intensity discharge lamp lighting device.
FIG. 1 is a graph showing load characteristics of a high-intensity discharge lamp lighting circuit means and a fluorescent lamp lighting circuit means.
In FIG. 1, the horizontal axis represents a current and the vertical axis represents a voltage.
In FIG. 1, also the curve A shows the load characteristics of the high-intensity discharge lamp stabilizer, and the curve B shows the load characteristics of the fluorescent lamp stabilizer. Here, as the rated operation points of the high-intensity discharge lamp of both stabilizers occur in a voltage range of 72-75 V and the current is in a range of 280-340 mA of the load characteristics, the rated operation points of the two types of the stabilizers are almost same.
However, the load characteristics of the high-intensity discharge lamp stabilizer, as shown in the characteristic curve A, the secondary open-circuit voltage V20 is relatively low, but the secondary short-circuit current Is is relatively high. This is because a higher pulse voltage is generated by an igniter at a starting operation, and then superposed to the output voltage of the stabilizer and lastly the superposed voltage is supplied to the lamp, so that, the stabilizer is not required to generate a much high voltage at the starting time. Further since the lamp voltage is low at the starting time in the high-intensity discharge lamp the lamp current is enlarged.
On the other hand, as shown in the curve B, in the load characteristics of the fluorescent lamp stabilizer, the secondary open-circuit voltage V20 is relatively high but the secondary short-circuit current is relatively slow. Then, the curve B smoothly extends across these two points. Accordingly, in the lower current region corresponding to the glow-arc transition time, e.g., in the region lower than the 30 mA, a secondary supply voltage is higher than the load characteristics of the high-intensity discharge lamp stabilizer.
Further, as the result of determining a glow power at the glow-arc transition, the glow power in the case of using the fluorescent lamp stabilizer was several times higher than that in the case of using the high-intensity discharge lamp stabilizer.
From the above facts, it is thought that the blackening is caused by the evaporation of the tungsten constituting electrodes under an excessive glow power.
On the other hand, it has been found that the blackening is influenced by a glow-arc transition time. That is, in a case of lighting a high-intensity discharge lamp provided with a silica glass discharge enclosure by a stabilizer, i.e., a lighting circuit means for conventional and typical coil and iron-core type high-intensity discharge lamp, a blackening occurring at a starting time is caused by spattering of tungsten electrodes due to mercury ions and rare gas ions during glow-discharge. Thus conventionally it was considered that the glow-arc transition time should be as short as possible for suppressing the blackening.
However, according to studies of the inventor, in the high-intensity discharge lamp provided with the light-transmissive ceramic discharge enclosure, it was found that in much shorter glow-arc transition time the blackening is accelerated due to a specific construction and a unique behavior of the discharge enclosure. On the contrary it was found that in much longer glow-arc transition time the blackening is also accelerated.
Here, a relation between the glow-arc transition time and the blackening will be explained.
That is, a high-intensity discharge lamp provided with a light-transmissive ceramic enclosure is comprised of an envelope defining a discharge space and small diameter cylinder portions communicating with the envelope. An electrode supporting portion is inserted inside the small diameter cylinder portion thus defining a narrow gap called a capillary between the inner wall of the small-diameter cylinder portion and the electrode supporting portion. When the high-intensity discharge lamp operates at a stable lighting condition, a surplus discharge agent resides at a liquid-phase in a bottom of the narrow gap and its surface presents a coldest portion in the lamp. Thus during a delighting of the high-intensity discharge lamp a large amount of the discharge agent deposits in the narrow gap and contacts to the electrode at the liquid-phase or a solid phase.
When the high-intensity discharge lamp is started, the whole electrode supporting portion in the narrow gap and the main portion of the electrode operate as an electrode and thus a glow discharge occurs around them. At this time, a part of a glow-arc transition power is consumed for evaporating the discharge agent. Thus almost the entire discharge agent temporarily evaporates. This delays a temperature rise to a glow-arc transition temperature required for the glow-arc transition and thus lengthens the glow-arc transition time. In case of the glow-arc transition time being much longer, the spattering of the electrode material become prominent and thus causes the blackening. The glow-arc transition time is also influenced by an amount and a kind of discharge agent. In the discharge agent a combination of Na, Tl and In or a combination of Na, Tl and Dy can be considered as the discharge agent, but they could not improve the glow-arc transition time.
On the other hand, it is considered to increase whole making voltage at a starting time for the to the high-intensity discharge lamp more than a minimum glow-arc transition power for moderately suppressing the glow-arc transition time. However, an excess supply of the glow power causes excessive heating of the electrode. Then an excess amount of electrode evaporation is caused which accelerates the blackening.
After the operation of the high-intensity discharge lamp has transferred from the glow discharge to the arc discharge, an arc-spot generates on the main portion of the electrode. Then, the surplus discharge agent again coagulates in the bottom of the narrow gap and resides at the liquid phase and its surface presents a coldest portion in the lamp. Then the high-intensity discharge lamp lights stably.
In a case of a high-intensity discharge lamp provided with a silica glass discharge enclosure, a coldest portion is formed on a part of the electrode, apart from a portion of the electrode in the envelope defining a discharge space. Thus it is considered that making the glow-arc transition time as short as possible is effective to suppress the blackening. To our knowledge, there is no document discussing the blackening in a case that a high-intensity discharge lamp is lighted by a lighting circuit means for use in a high-frequency lighting of a fluorescent lamp.
Furthermore, for lighting high-intensity discharge lamps it is required to always avoid an occurrence of acoustic resonance phenomenon. Here, the acoustic resonance phenomenon will be described. Conventionally a variety of proposals have been made for avoiding the acoustic resonance phenomenon. Among them, a simple and effective approach is to light high-intensity discharge lamps at an operation frequency distinctly lower than the resonance frequency of the high-intensity discharge lamps. The resonance frequency of the high-intensity discharge lamps varies in accordance with the shape and the size of the discharge space in the light-transmissive discharge enclosure. If in particular the shape of the discharge space is a complicated shape, e.g., a cylindrical shape, multiple modes of resonance frequencies yield. Therefore if the high-intensity discharge lamp is not lighted by an operation frequency distinctly lower than a fundamental mode of frequency, i.e., the lowest frequency among the multiple modes of resonance frequencies, it is impossible to avoid the acoustic resonance phenomenon.
Whereas, for satisfying the above conditions the operation frequency must be remarkably lowered. This is not advantageous for miniaturizing the lighting circuit means.
On the other hand, it is known that if high-intensity discharge lamps are lighted at an operation frequency 10 times higher than the fundamental mode frequency of the acoustic resonance phenomenon, the problem of the acoustic resonance will be avoided. However, when the operation frequency raises so high, radiation noises and line noises become intense. When if it is countered by an electromagnetic shielding, there occurs another problem that the size of the high-intensity discharge lamp eventually increases.
It is an object of the present invention to miniaturize a high-intensity discharge lamp and/or its lighting circuit.
Another object of the present invention is to provide a compact high-intensity discharge lamp lighting device and a lighting system using the discharge lamp which is able to reduce a blackening due to an evaporation of an electrode material at a glow-arc transition.
Still another object of the present invention to provide a compact high-intensity discharge lamp lighting device and a lighting system using the discharge lamp which are able to not only avoid an acoustic resonance phenomenon, but also miniaturize the size.
According to a first aspect of the present invention, a high-intensity discharge lamp lighting device has a high-intensity discharge lamp containing a light-transmissive discharge enclosure having an envelope defining a discharge space and a hollow member having an inner diameter smaller than the envelope, an elongate electrode being inserted into the hollow member of the light-transmissive discharge enclosure leaving a narrow gap from the inner wall of the hollow member and having a leading end protruding into the hollow member of the light-transmissive discharge enclosure, a lead-conductor having a leading end coupled to an base end of the electrode, a middle portion attached to the light-transmissive discharge enclosure and a base end exposing outward from the light-transmissive discharge enclosure, and discharge agent including at least neon and argon and filled into the light-transmissive discharge enclosure, and lighting circuit means having a load characteristics continuous from a secondary open-circuit voltage to a secondary short-circuit current for lighting the high-intensity discharge lamp at a high-frequency.
In the following descriptions, some definitions and their technical meanings are presented for following specific terms, unless otherwise specified.
 less than Light-transmissive Discharge Enclosure greater than 
The light transparent discharge enclosure, which is provided with an envelope and a hollow member, could be made of silica glass or light transparent ceramics. Here, the term xe2x80x9clight-transmissivityxe2x80x9d means a transmissivity allowing a light generated by a discharge to pass through outside a discharge lamp enclosure. Accordingly the term may represent not only a transparency but also a light-diffusiveness. Further, it is sufficient that at least the enclosure may have a light-transmissivity, or the envelope may have a light-shading ability.
The enclosure mainly holds a positive column generated across the electrodes during lighting. Further, the enclosure allows several shapes such as a sphere-shape, an oval-shape, or a fusi-shape.
The envelope is defined on one or both of the enclosure and generates a narrow gap between its inner surface and an electrode by inserting the electrode inside of it.
In case of the light transparent discharge enclosure being made of silica glass, since the silica glass can be processed by heating it could be sealed by the sealing means such as a pinch sealant.
However, in the case of a discharge lamp light transparent ceramic enclosure, since it cannot be processed by heated it could be sealed by sealant using ceramic sealing compound.
 less than Electrode greater than 
The electrode, which is elongated and is formed by a tungsten or doped tungsten, forms a narrow gap between the inner surface of the envelope by inserted into the envelope, and its top end protrudes inside of the hollow member.
The top end of the electrode could be wound by a coil of tungsten as occasionally needed in order to improve the discharge by enlarging the surface area.
The middle portion of the electrode is preferable to be a fixed size in order to form a narrow gap, i.e., a capillary as uniform as possible between the inner surface of the envelope of the discharge lamp light transparent enclosure with a space as equal as possible.
The base end of the electrode works for being fixed on a specific position to the discharge lamp light transparent enclosure and for leading the electric current from outside. In a case of a discharge lamp light-transmissive enclosure made of silica glass, the base end of the electrode is sintered to be connected electrically to the sealing metal film of the lead-conductor which is provided with sealing metal, and the top portion of it from the sintered portion could be held by the silica glass.
However, in a case of the discharge lamp light-transmissive enclosure made of the light-transmissive ceramic, the base end of the electrode is held electrically and mechanically by sintered to be fixed to the lead-conductor. Here, in order to buffer the heat at the sintering the material such as molybdenum could be interposed between the lead conductor and the base end of the electrode.
 less than Lead-conductor greater than 
The lead-conductor works for applying a voltage across the electrodes, supplying the electric current to the electrode, and sealing the discharge lamp light-transmissive enclosure. The top end of the lead-conductor is connected to the base end of the electrode, and the base end is exposed to outside of the discharge lamp light-transmissive enclosure. Further the phrase xe2x80x9cthe base end is exposed to the outside of the discharge lamp light-transmissive enclosurexe2x80x9d means that the may or may not protrudes outside of the discharge lamp light-transmissive enclosure, however, it has to face the outside while being supplied the current from outside.
Further the lead-conductor may be used for holding the whole high-intensity discharge lamp.
Furthermore, in case of the discharge lamp light-transmissive enclosure, the lead-conductor could be composed of sealing metal film and a lead-wire which top end is sintered with sealing metal.
In case of the discharge lamp light-transmissive made of the light-transmissive ceramic, the lead-conductor could be composed of the sealing metal rod, pipe, or coil of a niobium. In this case, since the niobium has an intense oxidation, an oxide-resistant conductor is connected to the lead-conductor and the lead-conductor has to be sealed by a sealant so as not to be exposed to the air when the high-intensity discharge lamp is turned on in a condition that it is exposed to the air.
 less than Discharge Agent greater than 
The discharge agent contains at least neon and argon as starting gas and buffer gas, and it is filled in the discharge lamp light-transmissive enclosure to put more than 1 pressure at lighting.
Further, the discharge agent is able to use the metal halide or mercury as a light radiating substance or buffer gas as occasionally needed.
Among the neon and the argon, the argon is mixed with the neon at the ration of 0.1-10% in the percent pressure.
Further, the neon and the argon are generally used at a charged gas pressure in a range of 50-580 torr. Here, if the charged gas pressure is less than 50 torr, the glow-arc transition time becomes longer, and the blackening due to the evaporation of the tungsten constituting electrode becomes significant. On the other hand, if the charged gas pressure exceeds 580 torr, the operating voltage of the high-intensity discharge lamp rises, and the glow power increases, and thus the object of the present invention cannot be achieved.
In case of using the metal halogen for the discharge agent, as halogen for constituting the metal halide, it is able to use one or a plurality from an iodine, a bromine, a chlorine, and fluorine.
The halide of light radiating metal is able to be selected from a group of known metal halides, in order to achieve a radiation provided with a desired lighting characteristics about a light color an average color rendering evaluation index Ra and a lighting efficiency, and further in response to the size and the input power of the light-transmissive discharge enclosure. For instance, one or a plurality of halides selected from a group of Na-halide, Li-halide, Sc-halide or rare-earth metal-halide could be used.
Further, halide of metal having a relatively high vapor pressure and radiating fewer amounts of visible lights or not radiating the visible lights, such as aluminum can be filled in the discharge enclosure, in place of a proper amount of mercury as a buffer pressure.
Furthermore, in place of neon or argon, other rare gas could be filled in a discharge lamp enclosure, as occasionally needed.
 less than Other Structures greater than 
(1) Outer Bulb
In the high-intensity discharge lamp according to the present invention, the light-transmissive discharge enclosure could be configured to a type of lighting exposed to the air. However, the light-transmissive discharge enclosure could be accommodated in the outer bulb by sealed. The high-intensity discharge lamp could have a directive light emission by making the inner wall of the outer bulb as a reflection surface at a focal point of alight source of the high-intensity discharge lamp.
(2) Reflector
The high-intensity discharge lamp according to the present invention is easy to collect light and advantageous in an optical configuration, since it could reduce the size of the light source. The light source could also be integrated with a reflector, as desired. In this case, the reflector could be formed on the inner wall of the outer bulb accommodating the high-intensity discharge lamp, or the high-intensity discharge lamp could be mounted on a separated reflector.
 less than Lighting Circuit Means greater than 
The load characteristics of the lighting circuit means regulated in the present invention is the same as the load characteristics represented in the case of the fluorescent lamp lighting circuit means. And the present invention is based on the new knowledge that when the high-intensity discharge lamp with a construction mentioned above is lighted by the lighting circuit means with such a load characteristics mentioned above, it does not generate a blackening at the starting operation.
Accordingly, a fluorescent lamp lighting circuit means can be used for the present invention. Of course it is needless to say that it is able to use the lighting circuit means, which is manufactured, for the high-intensity discharge lamp to satisfy a predetermined load characteristics specified in the present invention.
In the present invention, the term xe2x80x9chigh-frequencyxe2x80x9d means a frequency of 5 kHz or higher.
Further, in the present invention, the secondary open-circuit voltage V20 of the lighting circuit means is set up within the rage having relatively large flexibility for the discharge starting voltage of the high-intensity discharge lamp. That is, the ratio V20/Vs of the secondary opening discharge voltage V20 of the lighting circuit means to the discharge starting voltage Vs of the high-intensity discharge lamp can be set up in the following range.
110 less than V20/Vs less than 800
Here, since the discharge starting voltage Vs of the high-intensity discharge lamp statistically varies, it has to pay much attention to specify the discharge starting voltage Vs.
By the way, the principal circuit arrangement of the lighting circuit means may be any type if it has the load characteristics as mentioned above. For instance, the lighting circuit means may have a circuit arrangement constituted by principally a half-bridge inverter, a full-bridge inverter, a parallel inverter, a single-transistor type inverter such as a blocking oscillator inverter.
 less than Operation of the Aspect of the Invention greater than 
As a premise for effecting the blow-arc transition, the glow-arc discharge is needed to change from a usual glow discharge to an unusual glow discharge. A requirement for the glow-arc transition is not only a co-relation between the cathode voltage drop VK and the current density measured on electrode j/p2 (here, j denotes a glow discharge current (mA); and p denotes and electrode surface area (mm2)), but also varies in accordance with the kind of the buffer gas.
In the high-intensity discharge lamp lighting device according to this aspect of the present invention, the ionizing agent contains neon and argon as buffer gas. The electrode passes through the hollow member of the light-transmissive discharge enclosure. The lighting circuit means has a load characteristics similar to that of the fluorescent lamp lighting circuit means, i.e., a load characteristics continuous from the secondary open-circuit voltage to the secondary short-circuit wherein the secondary open-circuit voltage is close to the discharge starting voltage of the high-intensity discharge lamp. Thus, it is possible to lower the glow power at the glow-arc transition from a reason as described below.
(1) A current density measure on electrode decreases.
First, in the case that the buffer gas is comprised of both the neon and the argon, even though cathode voltage drops are the same, the glow current at the transition from the usual glow discharge to the unusual glow discharge decreases. So that, the glow power also decreases.
Further, at the glow discharge operation, since the mid-portion of the electrode which is exposed to the narrow gap of the envelope works as an electrode, like the edge portion of the electrode protruding to the hollow member of the discharge lamp light-transmissive enclosure, the effective surface of the electrode increases. Accordingly, even though the cathode voltage drop is fixed, the current density measured on the electrode is lowered.
(2) The discharge starting voltage is lowered.
In the case that the buffer gas is comprised of both the neon and the argon, since the discharge starting voltage is lowered as is already known in comparison to the case that only the argon is used as the buffer gas, it is able to lower the voltage which is supplied from the lighting circuit means at the glow-arc transition period, and thus the glow current is lowered. Here, the discharge starting voltage can be reduced to not greater than 2 kVp-p.
(3) The positive column loss increases.
If the buffer gas is comprised of both the neon and the argon, the positive column loss increases in comparison to the case that only the argon is used as the buffer gas, and thus a voltage is supplied to the electrodes.
As a result, the glow power is reduced to about ⅕ times in comparison to the case of argon only. It is found that the glow-arc transition time is extended for a moderate amount of time so that the evaporation of the tungsten on the electrode is depressed, and thus the blackening is remarkably reduced. Here, the glow-arc transition time can be nestled in a technically allowable range by optimizing the charged pressure of the buffer gas.
On one hand, since it forms a narrow gap between the inner surface of the envelope of the discharge lamp light-transmissive enclosure and the electrode, it is able to maintain a coldest portion of proper temperature at the interior portion of the narrow gap. Here, at the inner bottom of the narrow gap the non-evaporated discharge agent stays in a liquid-phase during the lighting of the lamp.
Accordingly, in the present invention, it is possible to obtain a compact high-intensity discharge lamp lighting device by using the compact lighting circuit means without using any igniter.
According to a second aspect of the present invention, a high-intensity discharge lamp lighting device has a high-intensity discharge lamp containing a light-transmissive discharge enclosure having an envelope defining a discharge space and a hollow member having an inner diameter smaller than the envelope, an elongate electrode being inserted into the hollow member of the light-transmissive discharge enclosure in leaving a narrow gap from the inner wall of the hollow member and having a leading end protruding into the hollow member of the light-transmissive discharge enclosure, a lead-conductor having a leading end coupled to a base end of the electrode, a middle portion attached to the light-transmissive discharge enclosure and a base end exposing outward from the light-transmissive discharge enclosure, and discharge agent including at least neon and argon and filled into the light-transmissive discharge enclosure, and lighting circuit means having load characteristics close to a discharge starting voltage of the high-intensity discharge lamp and continuous from a secondary open-circuit voltage to a secondary short-circuit current for lighting the high-intensity discharge lamp at a high-frequency.
In comparison to the first aspect of the invention, this second aspect of the invention is able to be configured so that the secondary open-circuit voltage of the lighting circuit means is close to the discharge starting voltage of the high-intensity discharge lamp, and the glow power at the starting operation time can be lowered.
The phrase xe2x80x9csecondary open-circuit voltage is close to the discharge starting voltagexe2x80x9d means that the secondary open-circuit voltage V20 is nestled in a range of 110-200% of the discharge starting voltage of the high-intensity discharge lamp.
In the case that the lamp power of the high-intensity discharge lamp is less than 50 W, the lighting circuit means is preferable to have a load characteristics in that the secondary opening discharge voltage V20 is less than 2.5 kVp-p, more preferably less than 2 kVp-p, and the secondary short-circuit current IS 1 s is less than 1.0 A.
According to a third aspect of the present invention, a high-intensity discharge lamp lighting device has a high-intensity discharge lamp containing a light-transmissive discharge enclosure having an envelope defining a discharge space and a hollow member having an inner diameter smaller than the envelope, an elongate electrode being inserted into the hollow member of the light-transmissive discharge enclosure leaving a narrow gap from the inner wall of the hollow member and having leading end protruding into the hollow member of the light-transmissive discharge enclosure, a lead-conductor having a leading end coupled to an base end of the electrode, a middle portion attached to the light-transmissive discharge enclosure and a base end exposing outward from the light-transmissive discharge enclosure, and discharge agent including at least neon and argon and filled into the light-transmissive discharge enclosure, and lighting circuit means having a high-frequency inverter provided with an LC resonator, for its key component:
As an inverter satisfying the requirements as mentioned above, it is able to be used a half-bridge inverter, a single-transistor type inverter, e.g., a blocking oscillator inverter, or a parallel inverter.
The oscillation control of the inverter may be done by either of a self-excitation or a separate-excitation. Furthermore, the operation frequency of the inverter may be made by either fixed or variable.
When the operation frequency of the inverter to the resonance frequency of the LC resonance circuit varies in accordance with a situation, the output voltage of the lighting circuit means can be controlled by changing the operation frequency of the inverter.
That is, if the operation frequency is brought closer to the resonance frequency of the LC resonance circuit at the starting operation, the output voltage rises, and thus the secondary open-circuit voltage can be brought closer to the discharge starting voltage of the high-intensity discharge lamp. On the other hand, if the operation frequency is brought away from the resonance frequency after lighting, the output voltage lowers. Accordingly, the secondary open-circuit voltage is able to be brought closer to the discharge starting voltage of the high-intensity discharge lamp, and the load characteristics of the lighting circuit means are able to smoothly extend from the secondary discharge voltage to the secondary short-circuit current.
And, when the operation frequency is fixed, it is able to control the output voltage of the lighting circuit means, by constituting the LC resonance circuit so as that its resonance frequency varies in response to a situation. That is, when the inductor L of the LC resonance circuit saturates at a no-load state and the inductance of the inductor L decreases under the saturation state, while the resonance frequency rises, so that the resonance frequency will be brought closer to the operation frequency. As a result, the output voltage of the lighting circuit means rises. Further, at a no-load state, the saturation state of the inductor L of the LC resonance circuit is released according to the lamp current, so that the resonance frequency alienates from the operation frequency and the output voltage lowers in accordance with the alienation.
In this invention, the circuit arrangement of the lighting circuit means is simplified, and thus it is possible to obtain the compact inexpensive high-intensity discharge lamp lighting device.
Further, since the lighting circuit means is provided with the LC resonance circuit, the waveform of the output voltage can be shaped to a sinusoidal waveform.
According to a fourth aspect of the present invention, the high-intensity discharge lamp of the high-intensity discharge lamp lighting device as defined in one of the above-described first through third aspects has, a light-transmissive ceramic discharge enclosure having an envelope defining a discharge space and a small diameter cylinder portion defining a hollow member having an inner diameter smaller than the envelope, an elongate electrode being inserted into the hollow member of the light-transmissive ceramic discharge enclosure in leaving a narrow gap from the inner wall of the hollow member and having leading end protruding into the hollow member of the light-transmissive ceramic discharge enclosure, a lead-conductor having a leading end coupled to a base end of the electrode for supporting the electrode and a base end exposing outward from the light-transmissive ceramic discharge enclosure, a sealing compound for sealing ceramics sealing the small diameter cylinder portion of the light-transmissive ceramic discharge lamp and the leading conductor together, and discharge agent including at least neon and argon and filled into the light-transmissive ceramic discharge enclosure.
 less than Discharge Lamp Light-transmissive Ceramic Enclosure greater than 
The phrase xe2x80x9cdischarge lamp light light-transmissive ceramic enclosurexe2x80x9d means a hermetic discharge lamp enclosure comprised of monocrystalline metal oxide, e.g., sapphire, polycrystalline metal oxide, e.g., semi-transparent aluminum oxide, and yttrium-aluminum garnet (YAG), yttrium oxide (YOX) and polycrystalline monoxide material, e.g., material having a light-transmissivity and heat-resistancy like aluminum nitride (AlN).
Further, in making the light-transmissive ceramic discharge enclosure, in case of the enclosure being sealed its two ends a centrally-located hollow member and a small diameter cylinder portion forming the envelope on the both end of the hollow member could be integrated together from the outset. However, it is also possible to produce an integrated light-transmissive ceramic discharge enclosure by separately pre-sintering individuals of a valve forming the enclosure and a pair of small diameter cylinders coupled to two opposite ends of the valve, then bonding them and lastly final-sintering the whole of them together. It is also possible to produce an integrated discharge enclosure by separately pre-sintering individuals of a cylinder forming a hollow member, a pair of end plates to be fit to both ends of the cylinder to close the cylinder and a pair of small diameter cylinders to be fit into central holes defined in the end plates to work as the small diameter cylinder portions, then assembling them together, and lastly final-sintering whole of them together.
In the case of a single closed-end structure, though the whole elements is able to be formed integrally from the outset in the same manner as the double closed-ends structure, individuals of a globe with an opening or a bottom-closed cylinder containing an opening and a cylinder for forming the small-diameter cylinder portion are provisionally sintered, and then fitting them desirably and lastly sintering whole of them to integrate. Further, the small-diameter cylinder portion could be made a single piece shared by a pair of electrodes, or alternatively it is also possible to prepare a pair of small-diameter cylinder portions. Here, when mounting the common piece small-diameter cylinder portion, upon an intermediate ceramic cylinder defined a pair of through-holes inserted into a small-diameter portion, and a pair of feed-conductors are inserted into the through-holes of the intermediate cylinder, and then sealed desirably, a required distance is ensured between the feed-conductor and the electrode.
Furthermore, in this aspect of the interior volume of the light-transmissive ceramic discharge enclosure is particularly effective at a small volume of less than 0.05 cc, or preferably less than 0.04 cc. But it is not necessarily limited to the specific volume. In this case the light-transmissive ceramic discharge enclosure has a whole length of 35 mm or less, preferably in a range of 10-30 mm.
 less than Lead Conductors greater than 
A lead conductor could use niobium, a tantalum, a titanium, a zirconium, a hafnium and a vanadium which are an electric leading metals having almost the same average thermal expansion coefficient as that of the light-transmissive ceramic. In a case of using aluminum oxide such as alumina ceramic as the material of the light-transmissive ceramic discharge enclosure, since the niobium and the tantalum have almost the same average thermal expansion coefficient as that of the aluminum oxide, they are suitable for sealing. In case of using the yttrium oxide and the YAG, there is no significant difference in their thermal expansion coefficients. In case of using the aluminum nitride, it is preferable to use the zirconium as the material of the sealable portion.
 less than Sealant for Ceramic Sealing Compound greater than 
The sealant for ceramic sealing compound is put between the lead-conductor and the small diameter cylinder portion at the end surface of the small diameter cylinder portion, and melts and enters into the gap between the small diameter cylinder portion and the lead-conductor. Then, the sealant for the ceramic sealing compound is cooled and hardened and seals the gap between the lead-conductor and the small diameter cylinder portion. The lead-conductor is fixed to a predetermined position by the sealant mentioned above.
The lead-conductor inserted in the small diameter cylinder portion is desirable to be sealed perfectly by the sealant mentioned above. Further, when the elongate base end portion of the electrode fixed to the lead-conductor is also covered by the sealant across the short distance more preferably across the extent of 0.2 to 0.3 mm, the lead-conductor is not easily eroded by discharge agent such as halogen.
 less than Operation of the Aspect of the Invention greater than 
When the elongate base end portion of the electrode is fixed on the end of the lead conductor to form the ceramic sealing compound sealant between the lead conductor and the small-diameter cylinder portion of the light-transmissive ceramic discharge enclosure the light-transmissive ceramic discharge enclosure is sealed and also a bottom sealed by the sealant is formed at the end of the envelope formed by the small-diameter cylinder portion, so as to form a narrow gap between the inner surface of the envelope and the electrode which is inserted into the small-diameter cylinder portion.
Since it uses the light-transmissive ceramic for the light-transmissive discharge enclosure, it is able to obtain the high-intensity discharge lamp lighting device provided with the high-intensity discharge lamp of high lamp efficiency and long life.
Further, the light-transmissive ceramic discharge enclosure does not transmit neon the neon is hard to disappear at long time lighting so as to work well in long time.
According to a fifth aspect of the present invention, the high-intensity discharge lamp of the high-intensity discharge lamp lighting device as defined in one of the above-described first through fourth aspects is characterized in that the high-intensity discharge lamp is charged with the discharge agent containing the neon and the argon with a gas pressure in a range of 100-200 torr.
The present invention limits a preferable charged gas pressure of the neon and the argon of the high-intensity discharge lamp.
That is, the glow-arc transition time and the extent of the blackening vary in accordance with starting gas and a charged pressure of the buffer gas. The more the charged gas pressure increases, the more the glow power increases, and the more the heating temperature of the electrode rises. As a result, the glow-arc transition time tends to be shorted.
On the other hand, if the charged gas pressure of the neon and the argon become excessive the blackening increases. While if the charged gas pressure decreases the evaporation of the electrode substance increases due to the increasing of the glow-arc transition time.
Accordingly, by limiting the charged gas pressure of the neon and the argon in the range as mentioned above, the glow-arc transition time will be in a range of 2-3 sec, and also the blackening is remarkably reduced. The glow-arc transition time in such a case resides in a tolerance in practical application.
According to a sixth aspect of the present invention, a high-intensity discharge lamp lighting device has a discharge lamp containing an envelope defining a discharge space, a light-transmissive ceramic discharge enclosure having a small diameter cylinder portion coupled to the envelope and an inner diameter smaller than the envelope, an elongate electrode being inserted into the small diameter cylinder portion leaving a narrow gap from the inner wall of the small diameter cylinder portion of the light-transmissive ceramic discharge enclosure, and discharge agent filled into the light-transmissive ceramic discharge enclosure, and lighting circuit means for lighting the high-intensity discharge lamp at a high-frequency, wherein a glow-arc transition time of the high-intensity discharge lamp is in a range of 0.5-3.0 sec.
The explanations about the light-transmissive ceramic discharge enclosure, the electrode, the feed-conductor and the lighting circuit means are eliminated since they are identical to those in the preceding aspects of the present invention.
 less than Discharge Agent greater than 
The discharge agent contains at least neon and argon as buffer gas, and it is filled in the discharge lamp light-transmissive ceramic enclosure to put more than 1 pressure at lighting, similar to the preceding embodiments. Further, the discharge agent is also able to use the metal halide or mercury as a light radiating substance or buffer gas, in similar to the preceding embodiments. The discharge agent is able to use the metal halide or mercury as a light radiating substance or buffer gas as occasionally needed. Further as the rare gas, a combination of neon and argon can be filled for reducing a glow current at a transition from a diameter cylinder portion coupled to the envelope and an inner diameter smaller than the envelope, an elongate electrode being inserted into the small diameter cylinder portion in leaving a narrow gap from the inner wall of the small diameter cylinder portion of the light-transmissive ceramic discharge enclosure, and discharge agent filled into the light-transmissive ceramic discharge enclosure, and lighting circuit means for lighting the high-intensity discharge lamp at a high-frequency, wherein a glow-arc transition time of the high-intensity discharge lamp is in a range of 0.5-3.0 sec. The explanations about the light-transmissive ceramic discharge enclosure, the electrode, the feed-conductor and the lighting circuit means are eliminated since they are identical as those in the preceding aspects of the present invention.
 less than Discharge Agent greater than 
The discharge agent contains at least neon and argon as buffer gas, and it is filled in the discharge lamp light-transmissive ceramic enclosure to put more than 1 pressure at lighting, in similar to the preceding embodiments. Further, the discharge agent is also able to use the metal halide or mercury as a light radiating substance or buffer gas, in similar to the preceding embodiments. The discharge agent is able to use the metal halide or mercury as a light radiating substance or buffer gas as occasion needed. Further as the rare gas, a combination of neon and argon can be filled for reducing a glow current at a transition from a normal glow discharge to an abnormal glow discharge, and for reducing the discharge starting voltage, i.e., for adjusting the glow-arc transition time. Further in this case, the argon is mixed with the neon at the ration of 0.1-10% in the percent pressure. Furthermore, the neon and the argon are generally used at a charged gas pressure in a range of 50-580 torr, preferably in a range of 100-200 torr. Here, if the charged gas pressure is less than 50 torr, the glow-arc transition time becomes longer, and the blackening due to the evaporation of the tungsten constituting electrode becomes significant. On the other had, if the charged gas pressure exceeds 580 torr, the operating voltage of the high-intensity discharge lamp rises, and the glow power increases.
 less than Glow-Arc Transition Time greater than 
In this aspect of the invention, the glow-arc transition time must be in a range of 0.5-3 sec. This glow-arc transition time is obtained by an average of five samples of measurements and each lowering point of lamp voltage waveform is counted by monitoring on an oscilloscope. Here the lowering point of lamp voltage waveform must be a lowering point when both electrodes carry out the glow-arc transition. Accordingly, when there is a time difference between the glow-arc transitions on the electrodes, a lowering point of the later occurrence of the glow-arc transition is effective.
By the way if the glow-arc transition time is less than 0,5 sec, a large amount of the glow-arc transition power time is supplied within a short time of period so as to cause an excessive heating of the electrode. Then the electrode is excessively evaporated. Therefore, improper blackening occurs at the starting time is accelerated, and the luminous flux retention lower too much.
If the glow-arc transition time becomes so long as to exceed 3.0 sec, the spattering of the electrode material becomes prominent.
So that, there improperly occurs that the blackening at the starting time is accelerated, and the luminous flux retention lowers.
If the glow-arc transition time is in a range of 0.6-3.0 sec, it is possible to ensure a luminous flux retention of 80% or more after the lighting time of 3,000 hrs. Here the lighting time means the time period for a cycle of 166 min of lighting and 16 min of delighting. Further, it is able to define the glow-arc transition time into the above range by properly setting the requirements of the high-intensity discharge lamp and/or its matching to the lighting circuit means.
 less than Operation of the Aspect of the Invention greater than 
In this aspect of the invention, as the glow-arc transition time of the high-intensity discharge lamp provided with the light-transmissive ceramic discharge enclosure is set to be in a prescribed range, a blackening at the starting time is reduced and thus a luminous flux retention can be raised.
Further, if the glow-arc transition time is less than 3 sec, the glow-arc transition time in such extent resides in an agreeable allowable range in practical application not making users fill discomfort.
According to a tenth aspect of the present invention, the high-intensity discharge lamp of the high-intensity discharge lamp lighting device as defined in one of the above-described first through ninth aspects is characterized by the fact that the high-intensity discharge lamp has a lamp power lower than 60 W.
Since the high-intensity discharge lamp is so compact, the present invention is suitable for the optical fibers and it limits the high-intensity discharge lamp lighting device which could be used in place of the halogen electric bulb by the lamp power.
Such a compact high-intensity discharge lamp could be more preferable if it has a following requirements. It is preferable if it satisfies whole requirements, however it allows one or some combinations of them.
(1) The relation between the diameter xc3x8s (mm) of the lead conductor and the diameter xc3x8s (mm) of the electrode makes the relation to satisfy the following formula.
xe2x80x830.2 less than xc3x8e/xc3x8s less than 0.6
In order to prevent the corrosion of the sealant by the halides by decreasing the temperature of the sealant of the ceramic sealing compound, and improve the lighting efficiency by increasing the temperature of the narrow gap, the heat resistance is decreased by thickening the lead conductor on one hand, and increasing the heat resistance of the electrode on the other hand. If the diameter ratio xc3x8e/xc3x8s is lower than 0.2 the electrode is much thinner. While if it is higher than 0.6, the temperature of the sealant and the narrow gap can not be maintained at a specific value.
(2) Relationship between the interior volume of the light-transmissive ceramic discharge enclosure and its linear transmittance; the interior volume of the light-transmissive ceramic discharge enclosure is set lees than 0.1 cc, or preferably lees than 0.05 cc, the average linear transmittance of the hollow member is set to 20xc2x0 r6 or more, and preferably to 30% or more.
It is assumed that the linear transmittance is measured in a wavelength of 550 nm. Here, the term xe2x80x9caverage linear transmittancexe2x80x9d means an average value of the linear transmittance data measured at five different sampling points.
In the case of the light-transmissive ceramic discharge enclosure having small interior volume as mentioned above, if the average linear transmittance of its hallow portion is 20% or more, it is able to enhance not only the optical efficiency (overall apparatus optical efficiency) including that of an optical system such as a reflector to be combined with the discharge lamp, but also to reduce occurrences of the cracks in the light-transmissive ceramic discharge enclosure.
Here, the interior volume of the light-transmissive ceramic discharge enclosure is measured is a following way. First, the enclosure is submerged in water to fill the water in the enclosure. Then the enclosure is drawn out from water after the openings of both the small diameter cylinder portions having been closed. Then the volume of the water in the enclosure is metered and measured.
(3) The overall length of the light-transmissive ceramic discharge enclosure; the overall length is made lees than 30 mm.
(4) Narrow gap the narrow gap is set less than 0.21 mm.
In order to obtain the high-intensity discharge lamp of compact lamp power lower than 60 w, long life and high lamp efficiency, it is found that it is unable to obtain a favorable discharge lamp even if the size of the conventional discharge lamp had been proportionally reduced.
So, by setting the narrow gap as mentioned above, the heat resistance of the electrode is increased, and the heat transmittance from the discharge plasma or the electrode is decreased, so as to decrease the temperature of the sealant. Thus, it does not cause a leak at the sealant.
According to an eleventh aspect of the present invention, a high-intensity discharge lamp lighting device has a high-intensity discharge lamp having a light-transmissive ceramic enclosure with a spherical envelope at a sphericity of 0.6 or more for defining a discharge apace, a pair of electrodes located in facing to an interior of the light-transmissive ceramic enclosure, and discharge agent including neon and argon and filled into the light-transmissive ceramic discharge enclosure, and lighting circuit means for lighting the high-intensity discharge lamp at an operating frequency in a range of 40-80 kHz.
 less than Light-transmissive Ceramic Discharge Enclosure greater than 
The light-transmissive ceramic discharge enclosure is distinctive in its enclosure being shaped spherically with a sphericity of 0.6 or more. The sphericity will be described in referenced to FIG. 2.
FIG. 2 is a drawing for explaining the sphericity of the enclosure of the light-transmissive ceramic discharge enclosure in the high-intensity discharge lamp according to the present invention.
In FIG. 2, 1 denotes a light-transmissive ceramic enclosure: 1a denotes an enclosure; 1b denotes a small diameter portion x denotes a central axis and y denotes an axis vertical to the central axis x.
The light-transmissive ceramic enclosure 1 is made of a 1 is light-transmissive ceramics, and having an overall length L.
The envelope 1a is located at a center of the light-transmissive ceramic enclosure 1 and shaped spherically at a prescribed sphericity R,B. The envelope 1a has a maximum inside diameter a, a maximum outside diameter Oa, and an axial length b along the central axis x.
The small diameter cylinder portions 1b are protruded integrally from the ends of the envelope 1a along the central axis x. The small diameter cylinder portions 1b are defined with through-holes 1b1 with lengths L1, L2, respectively along the central axis x. Further the through-holes 1b1 have inner ends communicating with the interior of the envelope 1a and outer ends communicating with the exterior.
Further electrodes as described later are inserted into the through-holes 1b1 of the small diameter cylinder portions 1b, thus narrow gap or so-called capillaries are defined between the inner wall of the small diameter cylinder portions 1b and the electrodes. The small diameter cylinder portions 1b are also used for sealing the light-transmissive ceramic enclosure 1.
Here, the sum of the respective lengths L1 and L2 of the small diameter cylinder portions 1b, i.e., L1+L2 equals to a subtraction of the axial length b1 of the envelope 1a from the overall length L of the light-transmissive ceramic enclosure 1.
Here, P1 denotes two intersections of the axis y sad the inner wall of the enclosure 1a; P2 denotes surfaces on the boundaries of the inner wall of the enclosure 1a and the small diameter cylinder portions 1b whereon lines 1 from the intersections P1 normally contact. Further, P3 denotes intersections of the lines 1 sad the central axis x. Then the axial length b of the enclosure In is given as the distance between both of the intersections P3.
Then a sphericity RB of the enclosure 1a is given by a following equation.
RB=a/b
Here a denotes a maximum interior diameter of the enclosure 1a, and b is the axial length of the enclosure 1.
The sphericity RB is brought closer to 1, when the boundaries of the of the inner wall of the enclosure 1a of the light-transmissive ceramic enclosure 1 and the small diameter cylinder portions 1b, i.e., the surfaces P2 are square-cornered, and the interior diameters of the through-holes 1b1 of the small diameter cylinder portions 1b are relatively small, and further the enclosure 1a is a perfect sphere. However, the sphericity RB varies with the curvature radius of the surfaces P2 and the interior diameters of the small diameter cylinder portions 1b, from its definition. Here, the curvature radius of the surfaces P2 varies under conditions of manufacturing methods of the light-transmissive ceramic discharge enclosure. The interior diameters of the through-holes 1b1 of the small diameter cylinder portions 1b are also influenced by a lamp design for the diameter of the electrode and the narrow gap. However, se they hardly influence on the resonance frequency, the sphericity RB in the present invention is defined as mentioned above in consideration of some degree of design flexibility. Further, although the shape of the envelope of the light-transmissive ceramic enclosure in the present invention is somewhat oblong in similar a spheroid, the shape can be considered as a sphere.
Further, if the sphericity RB exceeds 1, there is a range considered as a share oblong along the axis y than the axis x. Accordingly, the sphericity RB can be allowed to extent till generally about 1.2, but preferably 1.1
The structure of the light-transmissive ceramic enclosure is not specifically limited except the structure of the envelope.
 less than Other Structures greater than 
The explanations about the electrode, the discharge agent and the lamp power are eliminated since they are identical se those in the preceding aspects of the present invention.
 less than Lighting Circuit Means greater than 
Lighting circuit means generates an operation frequency in a range of 40-80 kHz for lighting high-intensity discharge lamps. As the operation frequency is irrelevant to a circuit arrangement, any type of circuit arrangement can be used for the lighting circuit means.
 less than Operation of the Aspect of the Invention greater than 
According to this aspect of the invention, the sphericity of the envelope of the light-transmissive ceramic enclosure has a sphere with the sphericity of 0.6 or more. The discharge agent includes neon and argon. The lamp power is lees than 50 W. And the operation frequency of the lighting circuit means is in a range of 40-80 kHz. Here as the resonance frequency of the high-intensity discharge lamp becomes sufficiently higher than the operation frequency, there is no acoustic resonance. Further as the operation frequency is in the above-described range, circuit components, in particular, windings are reduced in their size. Thus the operation frequency in the above-described range is effective to miniaturize the lighting circuit means. Further semiconductor switching elements used in the lighting circuit means for generating a high-frequency could be reduced in their cost, and able to obtain a high-frequency conversion efficiency due to a small switching loss.
According to a 12th aspect of the invention, in the high-intensity discharge lamp of the high-intensity discharge lamp lighting device as defined in the 11th aspect of the invention, it is characterized by that a glow-arc transition time of the high-intensity discharge lamp is in a range of 0.6-8.0 sec.
According to the glow-arc transition time in the above range, this aspect of the invention can provide a high-intensity discharge lamp which hardly cause such a blackening at the starting operation if a compact lighting circuit means like that used for fluorescent lamp is used for the lighting operation.
According to a 13th aspect of the invention, in the high-intensity discharge lamp of the high-intensity discharge lamp lighting device as defined in any one of the first, second, fourth, fifth to 12th aspects of the invention, it is characterized by that the lighting circuit means includes an LC resonance type high-frequency inverter.
According to this aspect of the invention, the lighting circuit means is able to generate a required starting voltage at a starting operation by a simple circuit arrangement. Further explanations of this aspect of the invention are eliminated since they are identical as those in the third aspect of the present invention. According to a 14th aspect of the invention, in the high-intensity discharge lamp of the high-intensity discharge lamp lighting device as defined in any one of the first to 13th aspects of the invention, it is characterized by that the lighting circuit means has a secondary no-load voltage in a range of 1.0-3.0 kVpp.
According to this aspect of the invention, the lighting circuit means with the secondary no-load voltage in that range is able to reliably start the high-intensity discharge lamp without an igniter.
Further as the secondary no-load voltage in that range the lighting circuit means is simplified its construction. For example, an LC resonant type high-frequency inverter is able to be used for easily obtaining a required secondary no-load voltage.
According to a 15th aspect of the invention, a lighting device is characterized by that it is comprised of a lighting system main body and a high-intensity discharge lamp as defined in any one of the first to 14th aspects of the invention.
In this aspect of the invention, the term xe2x80x9clighting devicexe2x80x9d a wide concept containing all of such devices using lights radiated by high-intensity discharge lamps for any purpose. For example, the lighting device according to this aspect of invention is able to apply for bulb-type high-intensity discharge lamps, lighting equipments, mobile-use headlights, optical fiber-use light sources, image projectors, photochemical devices, fingerprint discriminators, etc.
Here, the term xe2x80x9clighting device main bodyxe2x80x9d means reminders of the lighting device from which the high-intensity discharge lamp is removed.
Here, also the term xe2x80x9cbulb-type high-intensity discharge lampxe2x80x9d means a lighting device in which a high-intensity discharge lamp and a stabilizer thereof are integrated together, and a bulb-base is added thereto for receiving a commercial power. By loading the bulb-base to a corresponding lamp socket, this type of lamp device is used as if it is a incandescent lamp.
Further in case of constructing the bulb-type high-intensity discharge lamp, it is able to provide a reflector for obtaining a required light distribution from the high-intensity discharge lamp.
Furthermore, it is able to provide a light diffusion glove, or a cover for moderately reducing the brightness of the high-intensity discharge lamp.
Further, it is able to use a bulb-base having a desirable requirement. Accordingly, for replacing directly with conventional light lamps, a bulb-base the same as that of the conventional light lamps is able to be adopted.
Further, in the case of the lighting equipment, the lighting equipment can be a high-intensity discharge lamp provided with a lighting circuit means or a high-intensity discharge lamp provided with a bulb-type high-intensity discharge lamp not having a lighting circuit means. Further in the case of the lighting equipment provided with a lighting circuit means, the lighting circuit means can be located in the lighting equipment or as exterior, e.g., in ceilings.
Additional objects and advantages of the present invention will be apparent to persons skilled in the art from a study of the following description and the accompanying drawings, which are hereby incorporated in and constitute a part of this specification.